Submitted by Silvana Teresinha Dornelles Studzinski (sstudzinski) on 2015-10-09T13:32:14Z No. of bitstreams: 1 LACINA MARIA FREITAS TEIXEIRA_.pdf: 1605999 bytes, checksum: 3291f09168d3ebd23eab03339dd4bd64 (MD5) / Made available in DSpace on 2015-10-09T13:32:14Z (GMT). No. of bitstreams: 1 LACINA MARIA FREITAS TEIXEIRA_.pdf: 1605999 bytes, checksum: 3291f09168d3ebd23eab03339dd4bd64 (MD5) Previous issue date: 2015-03-30 / Nenhuma / O fitoplâncton é formado por organismos bastante diversos, de origem polifilética, composto principalmente por seres unicelulares autótrofos, que não são capazes de vencer as correntes (FALKOVISK; RAVEN, 1997). A dinâmica, distribuição e estrutura das comunidades fitoplanctônicas podem ser explicadas por uma variedade de fatores bióticos e abióticos relacionados à heterogeneidade ambiental. O presente estudo teve por principal objetivo avaliar a influência da heterogeneidade espacial e da escala temporal na estrutura e dinâmica da comunidade fitoplanctônica em um lago raso subtropical (Lagoa Mangueira, RS). O estudo ocorreu na Lagoa Mangueira, (sul do Brasil), que é um ecossistema aquático raso (Zmax = 7 m), extenso (90 km de extensão, 3 – 10 km de largura), polimíctico quente, considerado oligo-mestrófico, sob influência direta de um banhado adjacente ao norte e tem suas margens amplamente habitadas por macrófitas aquáticas, especialmente ao sul. Amostragens foram realizadas na subsuperfície da água, trimestralmente, por dois anos, em 19 pontos, compreendendo as zonas pelágica e litoral e as regiões sul, centro e norte da lagoa, para análises abióticas e biológicas. Foram ainda efetuadas amostragens em curtos intervalos de tempo durante 60 dias nas zonas pelágica e litoral na região sul. A estrutura da comunidade fitoplanctônica foi analisada a partir de medidas de clorofila a, biomassa, riqueza, diversidade de espécies, espécies descritoras e diversidade funcional. Cyanobacteria (ex. Chroococcus limneticus, Aphanocapsa conferta, Aphanothece smithii, Planktolyngbya contorta) foi o grupo mais representativo independente da região (sul, centro ou norte) ou zonas (litoral ou pelágica). Observou-se um claro padrão espacial em direção ao norte da lagoa, que apresentou maiores valores de biomassa total e clorofila. Contudo, a riqueza e as espécies descritoras não demonstraram padrão espacial nítido. A Análise de Redundância (RDA) evidenciou a forte organização temporal das espécies em função do cenário abiótico, indicando que o alto grau de variabilidade temporal devido à hidrodinâmica local foi o principal fator direcionador da estrutura da comunidade fitoplanctônica na Lagoa Mangueira no período de estudo. Os resultados da análise da diversidade funcional demonstraram que não houve organização espacial considerando-se as formas de vida e a estrutura de tamanho da comunidade fitoplanctônica no período estudado, embora os grupos funcionais fitoplanctônicos tenham respondido à variação nos recursos, especialmente aumentando sua variedade e contribuição nos meses de primavera e verão, segregando o norte da lagoa, independente das zonas estudadas (pelágica e litoral). Em curta escala de tempo a comunidade fitoplanctônica da região pelágica se mostrou mais equitativa do que a região litoral ao longo do tempo. A contribuição das espécies Chroococcus limneticus, Aphanocapsa conferta e Aphanothece smithii a partir do 9° dia na região pelágica e praticamente todo o período estudado na região litoral indicam que embora tenha se verificado a variação da precipitação e vento ao longo do tempo, estados de equilíbrio da comunidade fitoplanctônica em ambientes fortemente condicionados pela hidrodinâmica podem ocorrer. / The phytoplankton is formed by very different organisms of polyphyletic origin, composed mainly by autotrophic unicellular beings who are not able to overcome the current (FALKOVISK; RAVEN, 1997). The dynamics, distribution and structure of phytoplankton communities can be explained by a variety of biotic and abiotic factors related to environmental heterogeneity. The principal objective of the present study was evaluate the influence of spatial heterogeneity and the temporal, on the structure and dynamics of phytoplankton in a subtropical shallow lake (Mangueira Lagoon, RS). The study took place in the Mangueira Lagoon (southern Brazil), which is a shallow aquatic ecosystem (Zmax = 7 m) long (90 km long, 3-10 km wide), continuous hot polymictic, considered oligo-mesotrophic, under the direct influence of an adjacent wetland on the north and has its margins inhabited largely by aquatic macrophytes, especially in the south. Samples were taken in the subsurface of the water, quarterly, for two years, in 19 sites, including the pelagic and coastal zones and the southern, central and northern regions of the lagoon, for abiotic and biological analysis. Samples were also collected in short time intervals during 60 days in the pelagic and coastal zones in the south region. The structure of the phytoplankton community was analyzed by measures of chlorophyll a, biomass, richness, diversity of species, descriptors species and functional diversity. Cyanobacteria (e.g., Chroococcus limneticus, Aphanocapsa conferta, Aphanothece smithii, Planktolyngbya contorta) was the most representative group independently of region (southern, central or north) or zones (coastal or pelagic). It was observed a clear spatial pattern to the north of the lagoon, which showed higher values of total biomass and chlorophyll. However, richness and descriptors species showed no clear spatial pattern. The Redundancy Analysis (RDA) showed strong temporal organization of the species as a function of the abiotic scenario, indicating that the high degree of temporal variability due to the local hydrodynamics was the main determining factor of the structure of phytoplankton community in the Mangueira Lagoon during the period of study. The results of the analysis of functional diversity showed that there was no spatial organization considering the forms of life and the size structure of the phytoplankton community during the period of study, although the phytoplankton functional groups had responded to changes in resources, especially increasing its variety and contribution in the months of spring and summer, segregating the north of the lagoon, independently of the studied zones (pelagic and coastal). In short timescale the phytoplankton community from the pelagic area was more equitable than that from the coastal region over time. The contribution of the species Chroococcus limneticus, Aphanocapsa conferta and Aphanothece smithii from the 9th day in the pelagic region and practically the entire period studied in the coastal region indicate that despite the variation in precipitation and wind observed over time, steady-state of the phytoplankton community in environments strongly conditioned by hydrodynamics may occur.

Les mucilages pélagiques marins (MPM) sont des phénomènes mondiaux sporadiques et, dans certaines régions, chroniques dans les zones côtières. Ces agrégats gélatineux, enrichis en matière organique et en microorganismes, forment des écosystèmes marins autonomes transitoires allant de 0,5 cm à plusieurs kilomètres de long. Ils correspondent à des étapes évolutives de la neige marine non-sédimentée maintenue dans la zone photique. Durant les dernières décennies une intensification des apparitions des MPM ont été recensées. Ainsi, les MPM sont devenus un sujet de préoccupation pour les populations qui exploitent les ressources côtières et dans le contexte du fonctionnement global de l'écosystème. Malgré l’intérêt scientifique grandissant au cours des dernières décennies au sujet de ces phénomènes, notamment en mer Adriatique, les causes de formation, la dynamique et le rôle respectif des microorganismes dans de tels systèmes restent énigmatiques. La plupart des études réalisées sur les MPM étaient axées uniquement sur les communautés microbiennes eucaryotes par l’utilisation de techniques microscopiques. Or de nos jours, les méthodes moléculaires permettent de se concentrer également sur l'ensemble de la communauté, y compris les procaryotes. Afin d'approfondir notre compréhension de ces phénomènes nous avons étudié un type MPM qui est apparu de manière récurrente et abondante au cours de la dernière décennie dans le sud du Golfe de Gascogne (France), le «Liga». Dans un premier temps, nous avons étudié la formation de ce MPM au travers d’une année complète en suivant la dynamique des communautés archées, bactériennes et eucaryotes par la technique de T-RFLP, technique d’empreinte moléculaire ciblant la petite sous-unité du gène codant pour ARNr. Cette approche a révélé que les communautés microbiennes du Liga étaient différentes des communautés microbiennes marines pour les trois domaines du vivant, et que ces deux communautés étaient gouvernées par des paramètres environnementaux dont la variation était saisonnière. Les archées n’ayant pas pu être détectés dans le Liga, nous nous sommes focalisés sur la structure des communautés bactériennes et eucaryotes au moyen de technologies de séquençage à haut débit. Cette méthode a révélé que le Liga était principalement composé d'espèces marines, même si ces communautés étaient significativement différentes des espèces marines. Dans le Liga, les communautés eucaryotes étaient principalement composées de dinoflagellés, de zooplancton et de cnidaires. Les communautés bactériennes étaient principalement composées d’Alphaproteobacteria et de Gammaproteobacteria. La diversité fonctionnelle du Liga fraîchement formé a été également étudiée pendant les saisons d'apparition de ce phénomène, au printemps et à l'automne. Nous avons ainsi mis en évidence que les communautés microbiennes du Liga avaient potentiellement moins de capacités de résistance au stress et que ces communautés étaient potentiellement plus virulentes que les communautés microbiennes marines. / Marine pelagic mucilage (MPM) is worldwide phenomena occurring sporadically and, in certain regions, episodically in coastal areas. These gelatinous aggregates, enriched in organic matter and microorganisms, form autonomous transitory marine ecosystems ranging from 0.5 cm to several kilometers. They correspond to evolving stages originating from the non-settling early marine snow maintained in the photic zone. During the last decades intensification of MPM events have been noticed. They became a matter of concern both for populations exploiting coastal resources and in the context of global ecosystem functioning. Although increased scientific attention has been paid during last decades to these phenomena in specific areas such the Adriatic Sea, the causes of appearance, the dynamics, and the respective role of microorganisms in such systems remain enigmatic. Most of the studies performed on MPM focused on eukaryotic microbial communities using microscopic techniques. However molecular methods allow nowadays focusing also on the whole community including the prokaryotic part. In order to deeper our understanding of these phenomena we studied a MPM that occurred recurrently and more frequently during the last decade in the south of the Bay of Biscay (France), the “Liga”. In a first step we investigated the formation of this MPM through a complete year by following the dynamics of archaeal, bacterial and eukaryotic communities using T-RFLP fingerprinting targeting the small subunit of rRNA genes. This approach revealed that Liga’s microbial communities where different from marine microbial communities for the three domains of life and that both marine mucilage and marine communities were linked with seasonal patterns. As archaea were not found in the Liga, we focused on bacterial and eukaryotic communities’ structures through high throughput sequencing. The molecular composition revealed that the Liga was mainly composed of marine species although these communities were significantly different from marine species. In the Liga, eukaryotic communities were mainly composed of dinoflagellates, zooplankton and cnidarians species and bacterial communities were mainly composed of Alphaproteobacteria and Gammaproteobacteria. Functional diversity of freshly-formed Liga was targeted during its seasons of apparition, in spring and in autumn. We highlighted that Liga’s microbial communities had less potential capabilities to resist to stress conditions and that these communities were potentially more virulent than marine microbial communities.

La mise en place de réseaux écologiques est considérée comme l'un des moyens de pallier aux effets néfastes de la fragmentation sur la biodiversité. Dans les paysages agricoles, les éléments linéaires non cultivés peuvent constituer de larges réseaux, et jouer un rôle d'habitat-refuge et/ou de corridor de dispersion pour les espèces végétales. L'objectif de cette thèse est de comprendre quel rôle un réseau dense de fossés de drainage peut jouer dans le maintien et la dispersion d'espèces végétales dans un paysage agricole intensif du nord de la France. Nous avons également cherché à savoir dans quelle mesure les caractéristiques du paysage, la connectivité du réseau et les traits d'histoire de vie des espèces végétales impactent la dispersion des propagules au sein du réseau de fossés. Nos résultats montrent que les fossés jouent bien un rôle de corridor écologique pour les espèces végétales. En ciblant plus précisément les espèces hydrochores, nous avons démontré qu'elles dépendaient essentiellement de la composition et de la connectivité du réseau de fossés et des éléments immédiatement adjacents aux berges. Le réseau détermine également la structuration des flux de gènes chez deux espèces végétales de berges de fossés. Enfin, nos résultats montrent que la réponse des espèces à un gradient de connectivité du réseau dépend d'une combinaison de traits de dispersion, et qu'une diminution de cette connectivité entraîne une convergence fonctionnelle de ces traits à l'échelle de la métacommunauté. L'ensemble de ces résultats permet de mieux comprendre le rôle de corridor des fossés pour les espèces végétales, afin de permettre leur intégration au sein des projets de continuités écologiques dans les paysages agricoles. / The establishment of ecological networks is considered as one of the solutions to mitigate the negative effects of fragmentation on biodiversity. In agricultural landscapes, non-crop linear elements may form large networks, and constitute refuge habitats and/or dispersal corridors for plant species. The objective of this study is to understand which role may a dense drainage ditch network play for the maintenance and dispersal of plant species in an intensive agricultural landscape located in northern France. In addition, we also investigated the impact of landscape characteristics, network connectivity and plant species life-history traits on propagule dispersal within the ditch network. Our results indicate that ditches are indeed ecological corridors for plant species. By focusing more specifically on hydrochorous species, we demonstrated that they essentially depend on ditch network composition and connectivity and on elements immediately adjacent to the banks. The network also drives patterns of gene flow for two ditch bank plant species. Finally, our results also indicate that species’ response to ditch network connectivity depends on a combination of dispersal traits, and that connectivity reduction leads to functional convergence of those traits at the metacommunity scale. Together, these results provide a better understanding of the corridor role of ditches for plant species, in order to include these features into ecological network planning in agricultural landscapes.

Les prairies semi-naturelles constituent des espaces multifonctionnels susceptibles de rendre de nombreux services à la société. Ce sont en particulier des agro-écosystèmes favorables à l’expression d’une grande diversité floristique et faunistique permettant de concilier enjeux écologiques et agronomiques. Ce travail de thèse vise à analyser (i) l'influence des facteurs environnementaux sur l'assemblage des communautés in situ et (ii) les relations entre la structure fonctionnelle des assemblages (i.e. valeurs de traits agrégées et diversité fonctionnelle) et leurs performances (i.e. production de biomasse et digestibilité de cette biomasse). Cette étude s'appuie sur des approches expérimentales et de terrain dans les prairies humides pâturées du Marais Poitevin. Nos résultats montrent des réponses très différentes des traits aériens et racinaires étudiés aux gradients de stress et de perturbation rencontrés dans ces prairies. Ils ont également permis de mettre en évidence l'influence prépondérante des valeurs de traits agrégées sur la fourniture de services écosystémiques (i.e. productivité et digestibilité du fourrage), en accord avec la "Biomass ratio hypothesis" énoncée par Grime. L'influence du niveau de diversité fonctionnelle sur les services rendus par les assemblages varie selon le service considéré. Contrairement aux résultats attendus selon la "Diversity hypothesis" énoncée par Tilman, le niveau de diversité fonctionnelle est lié négativement à la productivité des assemblages. En revanche, un effet positif de la diversité fonctionnelle sur la digestibilité a été mis en évidence. Cette étude a par ailleurs permis de montrer un compromis entre la productivité des assemblages et la digestibilité de la biomasse produite dans ces prairies humides. Ce travail suggère que des outils de diagnostics de la valeur fourragère du couvert peuvent être construits sur la base de la structure fonctionnelle des assemblages, et ce avec un haut niveau de fiabilité. Il met également en avant les bénéfices agronomiques associés à l'hétérogénéité des couverts végétaux rencontrés dans ces prairies. / Semi-natural grasslands form multifunctional areas susceptible to serve the society from many aspects. Indeed, they are agro-ecosystems that promote expression of a large floristic and faunistic diversity, which allows conciliating ecologic and agronomic issues. This PhD work aims at analysing (i) influence of environmental factors on natural communities' assembly rules and (ii) the relationships between the functional structure of assemblages (i.e. community weighted mean trait values and functional diversity) and their performances (i.e. biomass production and its digestibility). This study is based on both experimental and field approaches in the Marais Poitevin wet grasslands. Our results show that the studied aerial and root traits display a wide diversity of answers to stress gradients and disturbances encountered in these grasslands. Our results also highlighted the crucial influence of community weighted mean trait values on provision of ecosystem services (i.e. forage productivity and digestibility), in agreement with the Biomass ratio hypothesis set out by Grime. The influence of the functional diversity level on services provided by the assemblages differs depending on the service considered. Contrary to the results expected according to the Diversity hypothesis of Tilman, the functional diversity level is negatively correlated with the productivity of the assemblages. However, our study points to a positive feedback between functional diversity and digestibility. Furthermore, this study demonstrated the existence of trade-off between the productivity of assemblages and the digestibility of biomass produced in these wet grasslands. This work suggests that highly reliable tools can be established, based on the functional structure of assemblages, to evaluate the feeding value of a vegetal cover. This work finally illustrates the agronomic benefits associated with heterogeneous vegetal covers encountered in these grasslands.

Ecossistemas aquáticos flutuam em torno de tendências, podendo ocorrer transições súbitas de um regime persistente para outro, alterando a viabilidade dos recursos ou dos parâmetros físico-químicos. Seguindo essa tendência, comunidades variam no tempo e no espaço como resultado de suas interações com o ambiente e com os outros organismos. Comunidades microbianas aquáticas são importantes componentes do metabolismo aquático, atuando na reciclagem de nutrientes pela remineralização e na transferência de biomassa pela alça microbiana. A compreensão da dinâmica funcional microbiana em lagos é uma importante ferramenta para o entendimento desses sistemas, uma vez que a funcionalidade e a composição microbiana podem refletir as condições gerais da lagoa em questão. Desse modo, no presente trabalho, foi utilizada a abordagem de impressões metabólicas da comunidade microbiana na Lagoa Mangueira, uma grande lagoa costeira, rasa e subtropical localizada no extremo sul do Brasil. Teve como objetivo avaliar, pioneiramente para essa região, a diversidade metabólica microbiana aquática através de padrões de consumo de fontes de carbono disponíveis, utilizando Biolog EcoplatesTM e verificar a existência de dinâmicas temporais e espaciais na preferência de consumo desses substratos. Foi observada heterogeneidade temporal e espacial na preferência de consumo de substratos ao longo da Lagoa. Tais preferências puderam ser representadas por diferentes substratos indicadores, associados às estações e aos locais da Lagoa. O consumo das fontes de carbono esteve relacionado com a variabilidade ambiental de fatores como turbidez, transparência da água, nutrientes, clorofila a, carbono orgânico temperatura. Isso evidencia que a dinâmica funcional foi influenciada pela dinâmica de nutrientes, pelos componentes de produtividade, pela sazonalidade e pela compartimentação da Lagoa. Nesse sentido, a investigação do consumo de fontes de carbono, no presente estudo, se mostrou um bom indicador da dinâmica funcional microbiana para ecossistemas aquáticos. / Aquatic ecosystems float around trends in which abrupt transitions can occur between persistents regimes, alterning the viability of the resources or the physical and chemical parameters. Following this trend, communities vary in time and space as a result of their interactions with the environment and other organisms. Microbial communities are important components in the aquatic metabolism, responsible for recycling of nutrients by remineralization, and transfering of biomass through the microbial food web. Understanding the functional microbial dynamics in lakes is an important tool to understand these systems, since the microbial composition and function may reflect the overall condition of the lake. The approach of metabolic fingerprint of microbial communities in shallow lakes was applied in the current study in Lake Mangueira, a costal and large subtropical shallow lake located in southern Brazil. The main goal was to evaluate, pioneered for this region, the heterotrophic microbial metabolic diversity through consumption patterns of available carbon sources using Biolog EcoplatesTM and verify the existence of temporal and spatial dynamics of consumption preference in these substrates. As a result, was observed temporal and spatial heterogeneity of substrate consumption preference among the Lake. Such preferences were represented by different substrate indicators, associated with seasons and sites within the Lake. The substrate utilization was related to environmental variability of factors as turbidity, water transparence, nutrients, chlorophyll a, organic carbon, water temperature. This is evidence that the functional dynamic was influenced by nutrients dynamic, production component, seasonality and compartimentation. In this way, carbon source utilization approach was a good indicator of functional dynamics in the present study to aquatic ecosystems.

Malgré l'importance reconnue des forêts tropicales humides dans la régulation du climat et du cycle global du carbone, la biogéochimie des forêts tropicales reste moins bien appréhendée que celle d'autres biomes. En particulier, il existe encore de larges incertitudes quant aux limitations nutritives des processus ou encore sur le rôle de la diversité pour les fonctions écosystémiques. La diversité spécifique élevée des arbres de forêt amazonienne se traduit localement par une forte hétérogénéité de la qualité des apports de litière foliaire, ces apports constituant une ressource primordiale d'énergie et de nutriments pour les organismes saprophages. Cependant les conséquences d'une telle hétérogénéité des litières pour le fonctionnement souterrain sont encore peu connues dans ce milieu. L'objectif de cette thèse est d'établir une compréhension mécaniste des effets de la qualité des apports de litière ainsi que du rôle de leur diversité sur la décomposition. J'ai combiné des fertilisations factorielles de carbone (C), d'azote (N) et de phosphore (P) à l'utilisation d'une large gamme de stœchiométrie C : N : P des litières (issues de différentes espèces d'arbres) en forêt tropicale de Guyane française et en laboratoire pour évaluer la nature et l'étendue des contraintes énergétiques et nutritives imposées par la qualité des litières sur les activités des décomposeurs. Bien que la perte en masse des litières dans ce système d'étude apparait largement expliquée par la qualité des différentes formes de C des litières, suggérant un fort contrôle de la disponibilité en énergie sur la décomposition, les ajouts externes de C n'ont pas permis de mettre en évidence cette apparente contrainte énergétique. Cependant, je montre que la décomposition des litières tropicales est limitée conjointement par N et P, et que l'amplitude de cette co-limitation est fortement reliée à la disponibilité en P des litières ainsi qu'à leur stœchiométrie N : P. Ainsi, même si le P apparaît plus profondément limitant dans ce système (en accord avec l'hypothèse généralement admise d'un fort déficit en P en forêt tropicale humide), l'accès à l'N foliaire semble également contraindre la décomposition. Je mets également en évidence des effets de diversité des mélanges de litières, pour la plupart synergiques (les taux de décomposition observés des mélanges étaient généralement plus élevés que ceux prédits à partir des taux de décomposition des espèces seules) et largement amplifiés par la présence de la faune détritivore. De plus, en présence de faune, il apparait qu'une forte dissimilarité stœchiométrique dans les mélanges de litières favorise des effets synergiques. Autrement dit, l'association de litières ayant des stœchiométries dissimilaires semble favoriser un meilleur équilibre nutritionnel pour la faune saprophage, stimulant ainsi la décomposition. Finalement, je montre que ces effets synergiques dans les mélanges sont renforcés à travers les effets à long terme des apports de litières issus des différentes espèces d'arbres contribuant à ces mélanges. Ce résultat suggère que la complémentarité de l'utilisation des ressources émerge à travers des interactions à long terme entre les arbres et les organismes décomposeurs. / The high tree species diversity in Amazonian rainforest translates into a high variation of leaf litter quality input to the soil. These inputs constitute a major resource of nutrients and energy for saprophageous organisms, particularly in tropical rainforests growing on old and highly weathered soils and consequently impoverished in rock-derived mineral nutrients. However the consequences of such leaf litter heterogeneity for belowground functioning are still poorly understood. In this thesis, I aim to develop a better mechanistic understanding of leaf litter quality effects and litter diversity on decomposition. Using a factorial fertilization of carbon (C), nitrogen (N), phosphorus (P) and a wide range of leaf litter C : N : P stoichiometries (derived from different tree species) in French Guiana rainforest and in laboratory, I aim to assess the nature and the extent of energetic and nutritional constraints imposed by litter quality on decomposer activities. Although the litter mass loss in this study system is greatly explained by the litter C quality, suggesting a strong control of energy availability on decomposition, external C additions do not alleviate this apparent energetic constraint. However, I find that litter decomposition is conjointly limited by N and P and that the extent of this NP co-limitation is widely related to leaf litter P content and to litter N : P stoichiometry. Thus, even if P appears more profoundly limiting in this system (in accordance to the well-recognized P deficiency hypothesis in tropical rainforest), the litter N access seems also constrain the decomposition. Moreover, I find significant litter diversity effects in litter mixtures and most of them are synergistics (observed mass loss in mixture was more often higher than predicted mass loss on the basis of single species decomposition). These litter diversity effects are largely higher in presence of soil fauna and increase with stoichiometric dissimilarity in mixtures. In other words, the association of stoichiometrically dissimilar litter appear promote a better nutritional balance for the saprophageaous fauna, and thus, stimulate the decomposition. Finally, I show that synergistic effects in mixtures are reinforced toward long-term presence of tree species contributing to the litter mixtures. This result suggest that complementarity effects on mixed litter decomposition may emerge through long-term interactions between aboveground and belowground biota.

This doctoral dissertation was produced in a cooperation between Halmstad University (Wetland Research Centre, School of Business and Engineering) and Lund University (Limnology &amp; Marine Biology, Department of Ecology). Abstract . Wetland creation at large, regional scales is implemented as a measure to abate the biodiversity loss in agricultural landscapes and the eutrophication of watersheds and coastal areas by non-point source nutrient pollution (mainly nitrogen). The consequences of creating many new wetlands for biodiversity conservation and nutrient reten- tion (ecosystem functioning) in agricultural landscapes are still relatively unknown, both on local (per wetland) and regional (per landscape) scales. In Sweden, wetland creation has progressed already since the 1990s, and by now larger numbers of created wetlands are present, mainly in the intensively farmed landscapes of southwestern Sweden. This thesis aimed to investigate the following aspects in these systems: (i) their large-scale effects on biodiversity, (ii) their functional diversity of bacterial denitrifiers, (iii) the abiotic and biotic influences on wetland ecosystem functioning, (iv) the potential for biodiversity-function links, and (v) the potential for functional links and joint functioning.(i) Created wetlands hosted diverse assemblages of macroinvertebrates and plants. They maintained a similar com- position and diversity as natural ponds in agricultural landscapes. The environmental conditions per wetland did hardly affect macroinvertebrate and plant assemblages, and the prerequisites for nutrient retention did neither. In landscapes were wetland creation efforts had increased the total density of small water bodies by more than 30%, macroinver- tebrate diversity of created wetlands was facilitated on both local and regional scales. (ii) Diverse communities of denitrifying bacteria with the capacity for conducting different denitrification steps (functional types) were present in all investigated wetlands. The richness of denitrifying bacteria communities was affected by nitrate concentration and hydraulic loading rate, which may potentially be relevant for the nitrogen retention function of created wetlands. The diversity across different functional types of bacterial denitrifiers increased with nitrate concentration. (iii) Both abiotic and biotic factors influenced ecosystem functions of created wetlands. Variation in nitrogen retention was associated to nitrate load, but even to vegetation parameters. In wetlands with constant nitrate load, planted emergent vegetation facilitated nitrogen retention compared to other vegetation types. In wetlands with variable loads, nitrogen retention was facilitated if nitrate load was high and many different vegetation types were present; nitrogen load could explain the majority of the variation in nitrogen retention compared to vegetation parameters. Phosporus retention of created wetlands was best explained by vegetation parameters. Litter decomposition was inhibited at high nitrate to phosphorus ratios. Methane production increased with age and decreased with plant cover. (iv) Biodiversity may facilitate wetland ecosystem functions, particularly in dynamic wetland ecosystems. Nitrogen retention increased with vegetation type diversity, phosphorus retention capacity with plant richness, and litter decomposition with macroinvertebrate diversity. (v) Created wetlands have the capacity of sustaining several parallel ecosystem services. Some wetland functions were coupled; nitrogen retention increased with fast litter decomposition. On the other hand, methane emission and nitro- gen retention were independent of each other, as were nitrogen and phosphorus retention.In conclusion, created wetlands have the potential to at least partly abate the lost biodiversity and multifunctionality caused by the past extensive destruction of natural wetlands in agricultural landscapes. / <p>[Paper II] Milenkovski S., Thiere G., Weisner S.E.B., Berglund O. &amp; Lindgren P.-E. Variation of eubacterial and denitrifying bacterial biofilm communities among constructed wetlands. Submitted manuscript. [Paper V] Thiere G. &amp; Weisner S.E.B. Influence of biotic and abiotic parameters on ecosystem functioning of created wetlands. Manuscript.</p>

What will happen to ecosystems if species continue to go extinct at the high rates seen today? Although ecosystems are often threatened by a myriad of physical or chemical stressors, recent evidence has suggested that the loss of species may have impacts on the functions and services of ecosystems that equal or exceed other major environmental disturbances. The underlying causes that link species diversity to ecosystem functioning include species niche complementarity, facilitative interactions, or selection effects, which cause process rates to be enhanced in more diverse communities. Interference competition, antagonistic interactions, or negative selection effects may otherwise reduce the efficiency or resource processing in diverse communities. While several of these mechanisms have been investigated in controlled experiments, there is an urgent need to understand how species diversity affects ecosystem functioning in nature, where variability of both biotic and abiotic factors is usually high. Species functional traits provide an important conceptual link between the effects of disturbances on community composition and diversity, and their ultimate outcomes for ecosystem functioning. Within this framework, I investigated relationships between the decomposition of leaf litter, a fundamental ecosystem process in stream ecosystems, and the composition and diversity of functional traits within the detritivore feeding guild. These include traits related to species habitat and resource preferences, phenology, and size. I focused on disentangling the biotic and abiotic drivers, including functional diversity, regulating ecosystem functioning in streams in a series of field experiments that captured real-world environmental gradients. Leaf decomposition rates were assessed using litter-bags of 0.5 and 10 mm opening size which allow the quantification of microbial and invertebrate + microbial contributions, respectively, to litter decomposition. I also used PVC chambers where leaf litter and a fixed number of invertebrate detritivores were enclosed in the field for a set time-period. The chemical characterisation of stream detritivores and leaf litter, by means of their nitrogen, phosphorus, and carbon concentration, was used to investigate how stoichiometric imbalance between detritivores and leaf litter may affect consumer growth and resource consumption. I found that the diversity and composition of functional traits within the stream detritivore feeding guild sometimes had effects on ecosystem functioning as strong as those of other major biotic factors (e.g. detritivore density and biomass), and abiotic factors (e.g. habitat complexity and agricultural stressors). However, the occurrence of diversity-functioning relationships was patchy in space and time, highlighting ongoing challenges in predicting the role of diversity a priori. The stoichiometric imbalance between consumers and resource was also identified as an important driver of functioning, affecting consumer growth rates, but not leaf decomposition rates. Overall, these results shed light on the understanding of species functional diversity effect on ecosystems, and indicate that the shifts in the functional diversity and composition of consumer guilds can have important outcomes for the functioning of stream ecosystems.

No description available.

Urbanisation is an ever-growing global phenomenon which creates altered environments characterised by increased human habitation, exotic species, impermeable surfaces, artificial structures, landscape fragmentation, habitat loss, and modified energy– and resource pathways. The vulnerable Rand Highveld Grassland vegetation unit in the Tlokwe Municipal area, South Africa, has been extensively degraded and transformed by urbanisation and agriculture. Only 1% of this endangered ecosystem is currently being actively conserved. Grassland fragments in urban areas are considered to be less species rich and less functional than their more “natural” counterparts, and are therefore not a priority for conservation. In this study the effects of landscape matrix quality on intra patch variables, namely plant species diversity and functional diversity, and fine-scale biogeochemical landscape function (as determined by Landscape Function Analysis or LFA) of 30 fragments of the Rand Highveld Grassland vegetation unit were explored. Four urbanisation measures (percentage urban land cover, percentage grass land cover, edge density, and density of people), acting as indicators for patterns and processes associated with urban areas, were calculated for matrix areas with a 500m radius surrounding each selected grassland fragment to quantify the position of each grassland remnant along an urban-to-rural gradient. Using the specific urbanisation measures, the grassland fragments were objectively classified into two classes of urbanisation, namely “rural/peri-urban” and “urban”, to allow for statistical comparisons between intra-patch variables for grassland remnants exposed to similar urbanisation pressures. Plant species composition and diversity were determined in the selected grassland fragments and nine functional traits were described for each species. Plant functional diversity was determined by five functional diversity indices, namely functional richness, evenness, divergence, dispersion, and specialisation. Fine-scale biogeochemical landscape function was determined by executing the LFA method. LFA assesses fine-scale landscape patchiness and 11 soil surface indicators to produce three main LFA parameters (stability, infiltration, and nutrient cycling), which indicates how well a system is functioning in terms of resource conservation and soil processes. Possible relationships between fine-scale biogeochemical landscape function and plant species- and functional diversity were also investigated. NMDS ordinations and basic statistics were used to determine trends and effects within the data. The results indicated that urban grassland remnants had lower mean plant species richness, Shannon species diversity (significantly), and Pielou species evenness than rural/peri-urban grassland fragments. Urban grassland fragments also contained significantly higher percentage of exotic species. Correlations were found between the four urbanisation measures and percentage species of the total species richness possessing certain functional attributes. This indicated that increased urbanisation may influence the species composition and the occurrence of certain plant traits in the selected grassland fragments. Urbanisation seems to have no effect on fine-scale landscape heterogeneity of the selected grassland fragments. Rural/peri-urban grassland fragments had higher infiltration capacity, nutrient cycling potential, and total SSA functionality (although not significantly), which may be ascribed to differences in management practices, such as mowing in urban areas and grazing in rural areas. Rand Highveld Grassland fragments in the urban landscape matrix of Potchefstroom city are just as conservable in terms of plant species diversity and functional diversity, as well as on a biophysical function level involving soil processes than rural/peri-urban grassland fragments. High plant species diversity and the presence of certain plant traits did not contribute to high soil surface stability, infiltration capacity, nutrient cycling potential and total soil surface functioning. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2013